The present invention relates to a process and an arrangement for determining the perfusion factor of a gas in a sample, and in particular to a process and an arrangement which determines the perfusion factor of oxygen which is dissolved in blood flowing through biological tissue.
It is already known to provide a device for polarographically measuring the amount of oxygen being diffused from the bloodstream of a sample. It is also known to provide a separate device for diathermically heating the sample portion and measuring flow of the blood stream through the sample by the heat supplied to the latter. For example, see Pfluegers Archiv 273,199-209/1961, Kanzow. However, in order to accurately determine the perfusion factor of the oxygen which is a function of both of these measurements, it is necessary to simultaneously measure both of these quantities at the same location.
It will be understood that the prior-art teaching of having separate devices is very disadvantageous since it is necessary for one to correctly position one of the devices, take a measurement, and -- after removal of the first device from the sample portion -- to correctly position the other device on the sample, and thereupon take another measurement. This interchange of devices must take place quickly inasmuch as the physiological measuring conditions vary as a function of time.
It is also known in the prior art U.S. Pat. No. 3,918,434 to measure the perfusion factor by using an electrical resistive wire heater which heats up a metallic member that is placed over the sample portion. However, this prior-art apparatus has the disadvantage that all of the heat flows through the interface between the metallic member and the sample portion. This means that the prior-art devices are strongly subject to rapid and frequent fluctuations in the contact resistance of the metallic member at the interface by virtue of the changing physiological conditions which, of course, leads to measurement errors.